1. Field of the Invention
The invention relates to a new process for the production of di-n-propylacetic acid from n-valeraldehyde.
2. Discussion of the Prior Art
Derivatives of di-n-propylacetic acid have gained great importance as psychopharmacologic drugs and antiepileptics. Several syntheses for the production of the acid have already been described.
In a known process, the starting material is malonic acid diethyl ester which is reacted initially with sodium methylate and then with allyl chloride to from di-allyldiethyl malonate. Saponification with sodium hydroxide gives the sodium salt of diallyl malonic acid which is thermally decarboxylated to form diallyl acetic acid and subsequently hydrogenated partially to form di-n-propylacetic acid. The process requires the use of expensive starting materials which are difficult to handle technically such as sodium methylate and allyl chloride.
Another mode of operation for the preparation of di-isopropylacetic acid is described by Sarel in J. Am. Chem. Soc. 78, 5416-5420 (1956). In this process, cyanoacetic acid ester is alkylated in the presence of sodium isopropylate by means of isopropylate by means of isopropyl iodide. This results in the formation of diisopropyl-cyanoacetic acid ester which is decarboxylated to form diisopropylacetonitrile. In further steps, the diisopropylacetonitrile is converted into diisopropylacetic acid via diisopropylacetic acid amide. The application of this reaction route to the synthesis of di-n-propylacetic acid results, however, into total yields of only 10 to 40% and, therefore, is commercially unattractive.
East German Pat. No. 129,776 describes a process for the production of di-n-propylacetic acid which starts from an ester of cyanoacetic acid. Reaction with n-propyl bromide or iodide in the presence of sodium-n-propylate, saponification of the di-n-propyl-cyanoacetic acid ester by means of caustic and acidification result in 2,2-di-n-propylcyanoacetic acid which is decarboxylated to form di-n-propylacetonitrile. The substituted acetonitrile is subsequently saponified with aqueous sulfuric acid via the acetamide to form di-n-propylacetic acid. This process also uses expensive starting materials and requires the use of reaction steps which cannot be carried out continuously. Moreover, since the hydrolysis of acetamide to form the acid is carried out in the presence of sodium nitrite, problems in connection with environmental pollution are encountered.
It is an object of this invention, therefore, to provide a process for the preparation of di-n-propylacetic acid which starts from inexpensive starting materials which are available in commercial amounts, comprises reaction steps which are readily carried out commercially and provides the desired product in satisfactory yields.